OF MICKOSCOPIC OBJECTS. 127 



plaints that this mixture becomes turbid with keeping ; but 



1 think this must only be the case when some impurity has 

 got into the bottle. 



CARBOLIC ACID.* The addition of a few drops of this to 

 distilled water prevents the growth of interfering substances 

 which would take place if pure water alone were used, and 

 is therefore valuable as a preservative fluid. The same 

 solution also is convenient, as it instantly kills infusoria, and 

 almost everything that has life ; and, indeed, is useful in 

 the student's gathering-bottles for the same reason. It is 

 very highly spoken of as forming one of the constituents in 

 the following formula for use in mounting soft animal 

 textures : 



Arsenious acid, 20 parts. 

 Crystallized carbolic acid, 10 parts. 

 Alcohol, 300 parts. 

 Distilled water, 700 parts. 



The Rev. W. W. Spicer, in his translation of Johann 

 Nave's work on Algae, recommends the following fluid for 

 their preservation : Pure alcohol, 3 parts ; distilled water, 



2 parts ; glycerine, 1 part. If the desmid or other alga 

 be placed in this fluid in a cell, and not covered by a glass 

 for a time, the water and alcohol will evaporate slowly, and 

 the mixture will become more dense in proportion, but quite 

 gradually, and therefore without any destructive influence 

 on the object. During this operation, water is withdrawn 

 from the frustule, and the glycerine, which is not volatile, 

 takes its place without causing any distortion of the object. 



CASTOR OIL. This is a very useful preservative for 

 crystals and other objects. Many salts are quite destroyed 

 when Canada balsam is used with them; but very few are 

 acted upon by this oil. To use it, it must be dropped in 

 sufficient quantity to cover the crystal or object to be 



* Dr. Grace Calvert stated at a meeting of the British Association, 

 that after careful experiments he finds carbolic acid " prevents the 

 development of protoplasmic and fungoid life." 



